1. Field of Invention
The present invention relates to a method for making an active device, and particularly to a thin film transistor and a fabrication method thereof.
2. Description of Related Art
Nowadays, following the advancement of semiconductor devices and display apparatuses, the multi-media technology has been well developed. As to displays, the Thin Film Transistor Liquid Crystal Display (TFT-LCD), having the advantages of higher image quality, better space efficiency, lower power consumption, and zero radiation, is gradually becoming a mainstream product of the display market, and thin film transistors are widely used in TFT-LCDs.
FIG. 1 is a cross-sectional view of a conventional thin film transistor. Referring to FIG. 1, the conventional thin film transistor 100 comprises a substrate 110, a gate 120, a dielectric layer 130, a channel layer 140, an ohmic contact layer 142, a source/drain 150, and a dielectric layer 160. The gate 120 is disposed on the substrate 110. The dielectric layer 130 covers the gate 120. The channel layer 140 is disposed on a part of the dielectric layer 130 above the gate 120. The ohmic contact layer 142 is disposed on the channel layer 140. The source/drain 150 is disposed on the ohmic contact layer 142. And the dielectric layer 160 is disposed on the substrate 110, covering the source/drain 150.
In detail, the source/drain 150 is composed of a barrier layer 152, a conductor layer 154 and a barrier layer 156, wherein the barrier layer 152 is disposed between the conductor layer 154 and the ohmic contact layer 142 and the barrier layer 156 is disposed on the conductor layer 154. It should be noted that a part of the conductor layer 154 is exposed.
To produce such a source/drain 150, after an ohmic contact layer 142 is formed, a barrier layer 152, a conductor layer 154 and a barrier layer 156 are formed over the substrate 110 in sequence. Then, parts of the barrier layer 152, the conductor layer 154 and the barrier layer 156 are respectively etched, thus forming a source/drain 150. Finally, a part of the ohmic contact layer 142 is etched.
If the material of the conductor layer 154 is Cu or Ni, the etching equipments may be contaminated by the atoms of the conductor layer 154, during the process of etching the conductor layer 154. Moreover, the atoms of the conductor layer 154 may diffuse into the channel layer 140 during the process of forming the ohmic contact layer 142, adversely affecting the electric characters of the conventional thin film transistor 100.